The concentration-density relation of galaxies in the Las Campanas Redshift Survey

We report the results of the evaluation of the "concentration-density" rela tion of galaxies in the local universe, taking advantage of the very large and homogeneous data set available from the Las Campanas Redshift Survey. T his data set consists of galaxies inhabiting the entire range of galactic e nvironments from the sparsest field to the densest clusters, thus allowing us to study environmental variations without combining multiple data sets w ith inhomogeneous characteristics. Concentration is quantified by the autom atically measured concentration index C, which is a good measure of a galax y's bulge-to-disk ratio. The environment of the sample galaxies is characte rized both by the three-space local galaxy density and by membership in gro ups and clusters. We find that the distribution of C in galaxy populations varies both with local density and with cluster/group membership: the fract ion of centrally concentrated galaxies increases with local galaxy density and is higher in clusters than in the field. A comparison of the concentrat ion-local density I:elation in clusters and the field shows that the two co nnect rather smoothly at the intermediate density regime, implying that the apparent cluster/field difference is only a manifestation of the variation with the local density. We conclude that the structure of galaxies is pred ominantly in influenced by the local density and not by the broader environ ments characterized by cluster/field memberships.